International science team finds most massive double neutron star system with distributed volunteer computing project Einstein@Home in data from the Arecibo radio telescope

Almost 25,000 light years away, two dead stars, each more massive than our Sun, but only 20 kilometers in diameter, orbit one another in less than five hours. This unusual pair of extreme objects, known as neutron stars, was discovered by an international team of scientists – including researchers from the Max Planck Institute for Gravitational Physics and the Max Planck Institute for Radio Astronomy – and by volunteers from the distributed computing project Einstein@Home. Their find is the latest addition to a short list of only 14 known similar binary systems, and it also is the most massive of those. Double neutron star systems are important cosmic laboratories that enable some of the most precise tests of Einstein’s theory of general relativity. They also play an important role as potential gravitational-wave sources for the LIGO detectors.

Neutron stars are the highly magnetized and extremely dense remnants of supernova explosions. Like a rapidly rotating cosmic lighthouse they emit beams of radio waves into space. If Earth happens to lie along one of the beams, large radio telescopes can detect the neutron star as a pulsating celestial source: a radio pulsar.

A rare pulsar breed

Most of the about 2500 known radio pulsars are isolated, i.e. spinning alone in space. Only 255 are in binary systems with a companion star, and only every 20th of those is in orbits with another neutron star.

“These rare double neutron star systems are unique laboratories for fundamental physics, enabling measurements that are impossible to obtain in any laboratory on Earth”, says Bruce Allen, director at the Max Planck Institute for Gravitational Physics in Hannover, director of Einstein@Home and co-author of the study published in The Astrophysical Journal. “That is why we need large telescopes like the Arecibo observatory and sensitive data analysis ‘machines’ like Einstein@Home to discover as many of these exciting objects as possible.”

The PALFA pulsar survey and Einstein@Home discover PSR J1913+1102
The new discovery was made in data from the Arecibo radio telescope. The PALFA consortium (PALFA: “Pulsar Surveys with the Arecibo L-Feed Array”), an international team of scientists, conducts a survey of the sky with the observatory to find new radio pulsars. The PALFA survey so far has discovered 171 radio pulsars. The data are also analyzed by the Einstein@Home distributed computing project, which has made 31 of these discoveries.

Einstein@Home aggregates the computing power provided by more than 40,000 volunteers from all around the world on their 50,000 laptops, PCs, and smartphones. The project is one of the largest distributed volunteer computing projects, and its computing power of 1.7 PetaFlop/s puts it among the 60 largest supercomputers in the world.

After the initial discovery of the binary system by Einstein@Home in February 2012, the PALFA researchers observed the system repeatedly with the Arecibo telescope to precisely measure the orbit of the radio pulsar, which spins once every 27.2 milliseconds (37 times each second). Their observations showed that the object called PSR J1913+1102 (this name encodes a sky position, the pulsar’s celestial “address”) consists of two stars orbiting one another in a little less than five hours in a slightly elliptical orbit.

From measuring how the pulsar rotates slightly slower over time, the scientists could also infer its magnetic field to be a few billion times that of our Earth. This is relatively weak for a neutron star and indicates an episode of matter accretion from the companion star in the distant past. This accretion episode, however, would have circularized the orbit, too. The observed ellipticity of the orbit is testament of the companion exploding in a supernova and leaving behind a second neutron star. The kick of the supernova explosion did not disrupt the binary system but made its orbits elliptical.

Record-breaking system shows Einstein’s relativity in action

Moreover, the research team measured an effect of Einstein’s general theory of relativity in the binary system. Like the orbit of Mercury around our Sun, the elliptical orbit of the radio pulsar rotates over time. But while Mercury’s orbit rotates by only 0.0001 degrees per year, J1913+1102’s orbit rotates 47,000 times faster: a full 5.6 degrees each year. The magnitude of this effect, known as relativistic periastron advance, depends on the combined mass of the radio pulsar and its companion, thereby allowing a measurement of this quantity.

“With a total mass of 2.88 times that of our Sun, our discovery breaks the current record for the total mass of the known double neutron star systems”, says Dr. Paulo Freire, researcher at the Max Planck Institute for Radio Astronomy in Bonn. “We expect that the pulsar is heavier than the companion star, but with our current observations we cannot yet determine the individual masses of the pulsar and its neutron star companion. However, continued observations will enable this measurement.”

If the pulsar indeed turns out to be substantially more massive than the companion, this system will be significantly different from all the other known double neutron star systems. In that case, it promises to become one of the best known laboratories for testing theories of gravitation alternative to Einstein's theory of general relativity.

Since the companion star also is a neutron star, it might also be detectable as a radio pulsar – provided its radio beam also sweeps over the Earth. But that does not seem to be the case for J1913+1102. The researchers painstakingly searched all their data for radio pulsations from the companion – but in vain. They did not find any sign of radio emission from the companion.

Potential LIGO sources

As the neutron stars orbit one another, their orbits shrink because the system emits gravitational waves. Measurements of this effect might allow to determine the individual masses of both the pulsar and its companion. Researchers hope to learn more about the little-known stellar evolution of such binary systems and the unknown properties of matter at the density of an atomic nucleus.

Discoveries like this one are also interesting for the era of gravitational-wave astronomy that began in September 2015 with the first direct detection of gravitational waves. “Finding double neutron stars systems similar to J1913+1102 is useful for the gravitational-wave science community. It helps us better understand how often these systems merge, and how often Advanced LIGO might detect the signals of merging neutron stars in the future”, concludes Prof. Michael Kramer, director at the Max Planck Institute for Radio Astronomy.

This graphic shows a frame from a computer simulation (main image)
and astronomical data (inset) of a distant galaxy undergoing an
extraordinary construction boom of star formation, as described in our press release. The galaxy, known as SPT0346-52, is 12.7 billion light years
from Earth. This means that astronomers are observing it at a critical
stage in the evolution of galaxies, about a billion years after the Big Bang.

Astronomers were intrigued by SPT0346-52 when data from the Atacama
Large Millimeter/submillimeter Array (ALMA) revealed extremely bright infrared emission from this galaxy. This suggested that the galaxy is undergoing a tremendous explosion of star birth.

However, another possible explanation for the excess infrared emission was the presence of a rapidly growing supermassive black hole
at the galaxy's center. In this scenario, gas falling towards the black
hole would become much hotter and brighter, causing surrounding dust
and gas to glow in infrared light.

To distinguish between these two possibilities, researchers used NASA's Chandra X-ray Observatory
and CSIRO's Australia Telescope Compact Array (ATCA), a radio
telescope. Neither X-rays nor radio waves were detected, so astronomers
were able to rule out a growing black hole generating most of the bright
infrared light. Therefore, they determined that SPT0346-52 is
undergoing a tremendous amount of star formation, an important discovery
for a galaxy found so early in the Universe.

The main panel of the graphic
shows one frame of a simulation produced on a supercomputer. The
distorted galaxy shown here results from a collision between two
galaxies followed by them merging.

Astronomers think such a merger could
be the reason why SPT0346-52 is having such a boom of stellar
construction. Once the two galaxies collide, gas near the center of the
merged galaxy (shown as the bright region in the center of the
simulation) is compressed, producing the burst of new stars seen forming
in SPT0346-52. The dark regions in the simulation represent cosmic dust
that absorbs and scatters starlight.

The inset in this graphic contains a composite image with X-ray data
from Chandra (blue), short wavelength infrared data from Hubble (green),
infrared light from Spitzer (red) at longer wavelengths, and infrared
data from ALMA (magenta) at even longer wavelengths. In the latter case
the light from SPT0346-52 is distorted and magnified by the gravity of
an intervening galaxy, producing three elongated images in the ALMA data
located near the center of the image.

SPT0346-52 is not visible in the
Hubble or Spitzer data, but the intervening galaxy causing the gravitational lensing
is detected. The bright galaxy seen in the Hubble and Spitzer data
slightly to the left of the image's center is unrelated to SPT0346-52.

There is no blue at the center of the image, showing that Chandra did
not detect any X-rays that could have signaled the presence of a
growing black hole. The ATCA data, not shown here, also involved the
non-detection of a growing black hole. These data suggest that
SPT0346-52 is forming at a rate of about 4,500 times the mass of the Sun
every year, one of the highest rates seen in a galaxy. This is in
contrast to a galaxy like the Milky Way that only forms about one solar
mass of new stars per year.

A paper describing these results, with first author Jingzhe Ma
(University of Florida), has been accepted for publication in The
Astrophysical Journal and is available online.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts,
controls Chandra's science and flight operations.

The constellation of Virgo
(The Virgin) is especially rich in galaxies, due in part to the
presence of a massive and gravitationally-bound collection of over 1300
galaxies called the Virgo Cluster.
One particular member of this cosmic community, NGC 4388, is captured
in this image, as seen by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3).

Located
some 60 million light-years away, NGC 4388 is experiencing some of the
less desirable effects that come with belonging to such a massive galaxy
cluster. It is undergoing a transformation, and has taken on a somewhat
confused identity.

While the galaxy’s outskirts appear smooth and featureless, a classic feature of an elliptical galaxy,
its centre displays remarkable dust lanes constrained within two
symmetric spiral arms, which emerge from the galaxy’s glowing core — one
of the obvious features of a spiral galaxy.
Within the arms, speckles of bright blue mark the locations of young
stars, indicating that NGC 4388 has hosted recent bursts of star
formation.

Despite the mixed messages, NGC 4388 is classified as a spiral galaxy.
Its unusual combination of features are thought to have been caused by
interactions between NGC 4388 and the Virgo Cluster.

Thursday, December 08, 2016

This view from NASA's Cassini spacecraft was obtained about half a day
before its first close pass by the outer edges of Saturn's main rings
during its penultimate mission phase. NASA/JPL-Caltech/Space Science
Institute.› Full image and caption

This collage of
images from NASA's Cassini spacecraft shows Saturn's northern
hemisphere and rings as viewed with four different spectral filters.
NASA/JPL-Caltech/Space Science Institute.› Full image and caption

NASA's Cassini spacecraft has sent to Earth its first views of
Saturn's atmosphere since beginning the latest phase of its mission. The
new images show scenes from high above Saturn's northern hemisphere,
including the planet's intriguing hexagon-shaped jet stream.

Cassini began its new mission phase, called its Ring-Grazing Orbits,
on Nov. 30. Each of these weeklong orbits -- 20 in all -- carries the
spacecraft high above Saturn's northern hemisphere before sending it
skimming past the outer edges of the planet's main rings.

Cassini's imaging cameras acquired these latest views on Dec. 2 and
3, about two days before the first ring-grazing approach to the planet.
Future passes will include images from near closest approach, including
some of the closest-ever views of the outer rings and small moons that
orbit there.

"This is it, the beginning of the end of our historic exploration of
Saturn. Let these images -- and those to come -- remind you that we've
lived a bold and daring adventure around the solar system's most
magnificent planet," said Carolyn Porco, Cassini imaging team lead at
Space Science Institute, Boulder, Colorado.

The next pass by the rings' outer edges is planned for Dec. 11. The
ring-grazing orbits will continue until April 22, when the last close
flyby of Saturn's moon Titan will once again reshape Cassini's flight
path. With that encounter, Cassini will begin its Grand Finale, leaping
over the rings and making the first of 22 plunges through the
1,500-mile-wide (2,400-kilometer) gap between Saturn and its innermost
ring on April 26.

On Sept. 15, the mission's planned conclusion will be a final dive
into Saturn's atmosphere. During its plunge, Cassini will transmit data
about the atmosphere's composition until its signal is lost.

Launched in 1997, Cassini has been touring the Saturn system since
arriving in 2004 for an up-close study of the planet, its rings and
moons. Cassini has made numerous dramatic discoveries, including a
global ocean with indications of hydrothermal activity within the moon
Enceladus, and liquid methane seas on another moon, Titan.

Careful study of large area of sky imaged by VST reveals intriguing result

Analysis of a giant new galaxy survey,
made with ESO’s VLT Survey Telescope in Chile, suggests that dark matter
may be less dense and more smoothly distributed throughout space than
previously thought. An international team used data from the Kilo Degree
Survey (KiDS) to study how the light from about 15 million distant
galaxies was affected by the gravitational influence of matter on the
largest scales in the Universe. The results appear to be in disagreement
with earlier results from the Planck satellite.

Hendrik Hildebrandt from the Argelander-Institut für Astronomie in Bonn, Germany and Massimo Viola from the Leiden Observatory in the Netherlands led a team of astronomers [1] from institutions around the world who processed images from the Kilo Degree Survey (KiDS), which was made with ESO’s VLT Survey Telescope
(VST) in Chile. For their analysis, they used images from the survey
that covered five patches of the sky covering a total area of around
2200 times the size of the full Moon [2], and containing around 15 million galaxies.

By exploiting the exquisite image quality available to the VST at the
Paranal site, and using innovative computer software, the team were
able to carry out one of the most precise measurements ever made of an
effect known as cosmic shear. This is a subtle variant of weak gravitational lensing,
in which the light emitted from distant galaxies is slightly warped by
the gravitational effect of large amounts of matter, such as galaxy clusters.

In cosmic shear, it is not galaxy clusters but large-scale structures
in the Universe that warp the light, which produces an even smaller
effect. Very wide and deep surveys, such as KiDS, are needed to ensure
that the very weak cosmic shear signal is strong enough to be measured
and can be used by astronomers to map the distribution of gravitating
matter. This study takes in the largest total area of the sky to ever be
mapped with this technique so far.

Intriguingly, the results of their analysis appear to be inconsistent with deductions from the results of the European Space Agency’s Planck satellite,
the leading space mission probing the fundamental properties of the
Universe. In particular, the KiDS team’s measurement of how clumpy
matter is throughout the Universe — a key cosmological parameter — is significantly lower than the value derived from the Planck data [3].

Massimo Viola explains: “This latest result indicates that dark
matter in the cosmic web, which accounts for about one-quarter of the
content of the Universe, is less clumpy than we previously believed.”

Dark matter remains elusive to detection, its presence only
inferred from its gravitational effects. Studies like these are the
best current way to determine the shape, scale and distribution of this
invisible material.

The surprise result of this study also has implications for our wider understanding of the Universe, and how it has evolved
during its almost 14-billion-year history. Such an apparent
disagreement with previously established results from Planck means that
astronomers may now have to reformulate their understanding of some
fundamental aspects of the development of the Universe.

Hendrik Hildebrandt comments: “Our findings will help to refine our theoretical models of how the Universe has grown from its inception up to the present day.”

The KiDS analysis of data from the VST is an important step
but future telescopes are expected to take even wider and deeper
surveys of the sky.

The co-leader of the study, Catherine Heymans of the University of Edinburgh in the UK adds: “Unravelling
what has happened since the Big Bang is a complex challenge, but by
continuing to study the distant skies, we can build a picture of how our
modern Universe has evolved.”

“We see an intriguing discrepancy with Planck cosmology at the
moment. Future missions such as the Euclid satellite and the Large
Synoptic Survey Telescope will allow us to repeat these measurements and
better understand what the Universe is really telling us,” concludes Konrad Kuijken (Leiden Observatory, the Netherlands), who is principal investigator of the KiDS survey.

Notes

[1] The internationalKiDS teamof researchers includes scientists from Germany, the Netherlands, the UK, Australia, Italy, Malta and Canada.

[2] This corresponds to about 450 square degrees, or a little more than 1% of the entire sky.

[3] The parameter measured is called S8.
Its value is a combination of the size of density fluctuations in, and
the average density of, a section of the Universe. Large fluctuations in
lower density parts of the Universe have an effect similar to that of
smaller amplitude fluctuations in denser regions and the two cannot be
distinguished by observations of weak lensing. The 8 refers to a cell
size of 8 megaparsecs, which is used by convention in such studies.

More Information

This research was presented in the paper entitled
“KiDS-450: Cosmological parameter constraints from tomographic weak
gravitational lensing”, by H. Hildebrandt et al., to appear in Monthly Notices of the Royal Astronomical Society.

ESO is the foremost intergovernmental astronomy organisation in
Europe and the world’s most productive ground-based astronomical
observatory by far. It is supported by 16 countries: Austria, Belgium,
Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy,
the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the
United Kingdom, along with the host state of Chile. ESO carries out an
ambitious programme focused on the design, construction and operation of
powerful ground-based observing facilities enabling astronomers to make
important scientific discoveries. ESO also plays a leading role in
promoting and organising cooperation in astronomical research. ESO
operates three unique world-class observing sites in Chile: La Silla,
Paranal and Chajnantor. At Paranal, ESO operates the Very Large
Telescope, the world’s most advanced visible-light astronomical
observatory and two survey telescopes. VISTA works in the infrared and
is the world’s largest survey telescope and the VLT Survey Telescope is
the largest telescope designed to exclusively survey the skies in
visible light. ESO is a major partner in ALMA, the largest astronomical
project in existence. And on Cerro Armazones, close to Paranal, ESO is
building the 39-metre European Extremely Large Telescope, the E-ELT,
which will become “the world’s biggest eye on the sky”.

Tuesday, December 06, 2016

The galaxy 3C438 and its cluster of galaxies as seen in the optical (left) and in X-rays by the Chandra X-ray Observatory (right). Astronomers have concluded that the hot gas is the result of a collision between two clusters of galaxies. Credit: X-ray: NASA/CXC/CfA/R.P.Kraft; Optical: Pal.Obs. DSS

Galaxy
clusters contain a few to thousands of galaxies and are the largest
bound structures in the Universe. Most galaxies are members of a
cluster. Our Milky Way, for example, is a member of the "Local Group," a
set of about fifty galaxies whose other large member is the Andromeda
galaxy. The closest large cluster of galaxies to us, about fifty
million light-years away, is the Virgo Cluster, with about 2000 members.

Clusters are believed to grow as the result of mergers between
smaller galaxy groups and from the accretion of gas and dark matter. The
energy released in these mergers is largely dissipated in the hot gas
within the cluster, where X-ray observations can spot evidence for
shocks and high temperatures. Mergers between two equally massive
galaxy clusters provide particularly important diagnostics since these
energetic collisions have the most dramatic and long-lasting effects.
These major mergers are relatively rare events, however. The Bullet
Cluster is one recently analyzed example, and because it also happens to
act as a gravitational lens for background galaxies, it became famous
for showing the distribution of its dark matter.

CfA astronomers Deanna Emery, Akos Bogdan, Ralph Kraft, Filipe
Andrade-Santos, Bill Forman, and Christine Jones, and another colleague
studied another major merger in the cluster around the galaxy 3C438.
Members of the team used the Chandra X-ray Observatory to examine the
hot cluster gas. Previous observations had concluded that activity was
due either to a supermassive black hole or from a massive merger, but
the two could not be distinguished. Using additional Chandra
observations and new calibration procedures, the scientists re-reduced
all the data. They found that the hot cluster gas extends over a
distance of about 2.5 million light-years and has brightness features
apparently caused by a merger bow shock. They are even able to
calculate the estimated relative velocity of the merger as about 2600
kilometers per second. Since few observations of bow shocks in clusters
have been made, this detection makes an important contribution to the
study of the dynamics of cluster mergers and how massive clusters may
have formed.

Monday, December 05, 2016

Artist's conception of the Spiderweb. In this image, the protogalaxies are shown in white and pink, and the blue indicates the location of the carbon monoxide gas in which the protogalaxies are immersed.
CREDIT: ESO/M. Kornmesser. This figure is licensed under CC BY 4.0 International License.

Astronomers studying a cluster of still-forming protogalaxies seen as
they were more than 10 billion years ago have found that a giant galaxy
in the center of the cluster is forming from a surprisingly-dense soup
of molecular gas.

"This is different from what we see in the
nearby Universe, where galaxies in clusters grow by cannibalizing other
galaxies. In this cluster, a giant galaxy is growing by feeding on the
soup of cold gas in which it is submerged," said Bjorn Emonts of the
Center for Astrobiology in Spain, who led an international research
team.

The scientists studied an object called the Spiderweb
Galaxy, which actually is not yet a single galaxy, but a clustering of
protogalaxies more than 10 billion light-years from Earth. At that
distance, the object is seen as it was when the Universe was only 3
billion years old. The astronomers used the Australia Telescope Compact
Array (ATCA) and the National Science Foundation's Karl G. Jansky Very
Large Array (VLA) to detect carbon monoxide (CO) gas.

The
presence of the CO gas indicates a larger quantity of molecular
hydrogen, which is much more difficult to detect. The astronomers
estimated that the molecular gas totals more than 100 billion times the
mass of the Sun. Not only is this quantity of gas surprising, they said,
but the gas also must be unexpectedly cold, about minus-200 degrees
Celsius. Such cold molecular gas is the raw material for new stars.

The
CO in this gas indicates that it has been enriched by the supernova
explosions of earlier generations of stars. The carbon and oxygen in the
CO was formed in the cores of stars that later exploded.

The
ATCA observations revealed the total extent of the gas, and the VLA
observations, much more narrowly focused, provided another surprise.
Most of the cold gas was found, not within the protogalaxies, but
instead between them.

"This is a huge system, with this molecular
gas spanning three times the size of our own Milky Way Galaxy," said
Preshanth Jagannathan, of the National Radio Astronomy Observatory
(NRAO) in Socorro, NM.

Earlier observations of the Spiderweb,
made at ultraviolet wavelengths, have indicated that rapid star
formation is ongoing across most of the region occupied by the gas.

"It appears that this whole system eventually will collapse into a single, gigantic galaxy," Jagannathan said.

"These
observations give us a fascinating look at what we believe is an early
stage in the growth of massive galaxies in clusters, a stage far
different from galaxy growth in the current Universe," said Chris
Carilli, of NRAO.

The astronomers reported their findings in the December 2 issue of the journal Science.

The
National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.

Friday, December 02, 2016

This delicate blue group of stars — actually an irregular galaxy named IC 3583 — sits some 30 million light-years away in the constellation of Virgo (The Virgin).

It may seem to have no discernable structure, but IC 3583 has been found to have a bar of stars running through its centre. These structures are common throughout the Universe, and are found within the majority of spiral, many irregular, and some lenticular galaxies. Two of our closest cosmic neighbours, the Large and Small Magellanic Clouds,
are barred, indicating that they may have once been barred spiral
galaxies that were disrupted or torn apart by the gravitational pull of
the Milky Way.

Something similar might be happening with IC 3583. This small galaxy is
thought to be gravitationally interacting with one of its neighbours,
the spiral Messier 90.
Together, the duo form a pairing known as Arp 76. It’s still unclear
whether these flirtations are the cause of IC 3583’s irregular
appearance — but whatever the cause, the galaxy makes for a strikingly
delicate sight in this NASA/ESA Hubble Space Telescope image, glimmering
in the blackness of space.

New observations from the NASA/ESA Hubble
Space Telescope have revealed the intricate structure of the galaxy NGC
4696 in greater detail than ever before. The elliptical galaxy is a
beautiful cosmic oddity with a bright core wrapped in system of dark,
swirling, thread-like filaments.

NGC 4696 is a member of the Centaurus galaxy cluster,
a swarm of hundreds of galaxies all sitting together, bound together by
gravity, about 150 million light-years from Earth and located in the constellation of Centaurus.

Despite the cluster’s size, NGC 4696 still manages to stand out from
its companions — it is the cluster’s brightest member, known for obvious
reasons as the Brightest Cluster Galaxy . This puts it in the same category as some of the biggest and brightest galaxies known in the Universe.

Even if NGC 4696 keeps impressive company, it has a further
distinction: the galaxy’s unique structure. Previous observations have
revealed curling filaments that stretch out from its main body and carve
out a cosmic question mark in the sky (heic1013), the dark tendrils encircling a brightly glowing centre.

An international team of scientists, led by astronomers from the
University of Cambridge, UK, have now used new observations from the
NASA/ESA Hubble Space Telescope to explore this thread-like structure in
more detail. They found that each of the dusty filaments has a width of
about 200 light-years, and a density some 10 times greater than the
surrounding gas. These filaments knit together and spiral inwards
towards the centre of NGC 4696, connecting the galaxy’s constituent gas
to its core.

In fact, it seems that the galaxy’s core is actually responsible for
the shape and positioning of the filaments themselves. At the centre of
NGC 4696 lurks an active supermassive black hole. This floods the
galaxy’s inner regions with energy, heating the gas there and sending
streams of heated material outwards.

It appears that these hot streams of gas bubble outwards, dragging
the filamentary material with them as they go. The galaxy’s magnetic
field is also swept out with this bubbling motion, constraining and
sculpting the material within the filaments.

At the very centre of the galaxy, the filaments loop and curl inwards in an intriguing spiral shape, swirling around the supermassive black hole at such a distance that they are dragged into and eventually consumed by the black hole itself.

Understanding more about filamentary galaxies such as NGC 4696 may
help us to better understand why so many massive galaxies near to us in
the Universe appear to be dead; rather than forming newborn stars from
their vast reserves of gas and dust, they instead sit quietly, and are
mostly populated with old and aging stars. This is the case with NGC
4696. It may be that the magnetic structure flowing throughout the
galaxy stops the gas from creating new stars.

More Information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

VLT observations of neutron star may confirm 80-year-old prediction about the vacuum

By studying the light emitted from an
extraordinarily dense and strongly magnetised neutron star using ESO’s
Very Large Telescope, astronomers may have found the first observational
indications of a strange quantum effect, first predicted in the 1930s.
The polarisation of the observed light suggests that the empty space
around the neutron star is subject to a quantum effect known as vacuum
birefringence.

A team led by Roberto Mignani from INAF Milan (Italy) and from the University of Zielona Gora (Poland), used ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile to observe the neutron star RX J1856.5-3754, about 400 light-years from Earth [1].

Despite being amongst the closest neutron stars, its extreme dimness
meant the astronomers could only observe the star with visible light
using the FORS2 instrument on the VLT, at the limits of current telescope technology.

Neutron stars are the very dense remnant cores of massive stars — at
least 10 times more massive than our Sun — that have exploded as supernovae
at the ends of their lives. They also have extreme magnetic fields,
billions of times stronger than that of the Sun, that permeate their
outer surface and surroundings.

These fields are so strong that they even affect the properties of
the empty space around the star. Normally a vacuum is thought of as
completely empty, and light can travel through it without being changed.
But in quantum electrodynamics
(QED), the quantum theory describing the interaction between photons
and charged particles such as electrons, space is full of virtual
particles that appear and vanish all the time. Very strong magnetic
fields can modify this space so that it affects the polarisation of
light passing through it.

Mignani explains: “According to QED, a highly magnetised vacuum
behaves as a prism for the propagation of light, an effect known as
vacuum birefringence.”

"This effect can be detected only in the presence of enormously
strong magnetic fields, such as those around neutron stars. This shows,
once more, that neutron stars are invaluable laboratories in which to
study the fundamental laws of nature." says Roberto Turolla (University of Padua, Italy).

After careful analysis of the VLT data, Mignani and his team detected linear polarisation — at a significant degree of around 16% — that they say is likely due to the boosting effect of vacuum birefringence occurring in the area of empty space surrounding RX J1856.5-3754 [2].

Vincenzo Testa (INAF, Rome, Italy) comments: "This is the
faintest object for which polarisation has ever been measured. It
required one of the largest and most efficient telescopes in the world,
the VLT, and accurate data analysis techniques to enhance the signal
from such a faint star."

"The high linear polarisation that we measured with the VLT can’t
be easily explained by our models unless the vacuum birefringence
effects predicted by QED are included," adds Mignani.

This VLT study is the very first
observational support for predictions of these kinds of QED
effects arising in extremely strong magnetic fields," remarks Silvia Zane (UCL/MSSL, UK).

Mignani is excited about further improvements to this area of study that could come about with more advanced telescopes: “Polarisation measurements with the next generation of telescopes, such as ESO’s European Extremely Large Telescope, could play a crucial role in testing QED predictions of vacuum birefringence effects around many more neutron stars.”

This measurement, made for the
first time now in visible light, also paves the way to similar
measurements to be carried out at X-ray wavelengths," adds Kinwah Wu (UCL/MSSL, UK).

More Information

This research was presented in the paper entitled “Evidence
for vacuum birefringence from the first optical polarimetry measurement
of the isolated neutron star RX J1856.5−3754”, by R. Mignani et al., to
appear in Monthly Notices of the Royal Astronomical Society.

ESO is the foremost intergovernmental astronomy
organisation in Europe and the world’s most productive ground-based
astronomical observatory by far. It is supported by 16 countries:
Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland,
Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden,
Switzerland and the United Kingdom, along with the host state of Chile.
ESO carries out an ambitious programme focused on the design,
construction and operation of powerful ground-based observing facilities
enabling astronomers to make important scientific discoveries. ESO also
plays a leading role in promoting and organising cooperation in
astronomical research. ESO operates three unique world-class observing
sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO
operates the Very Large Telescope, the world’s most advanced
visible-light astronomical observatory and two survey telescopes. VISTA
works in the infrared and is the world’s largest survey telescope and
the VLT Survey Telescope is the largest telescope designed to
exclusively survey the skies in visible light. ESO is a major partner in
ALMA, the largest astronomical project in existence. And on Cerro
Armazones, close to Paranal, ESO is building the 39-metre European
Extremely Large Telescope, the E-ELT, which will become “the world’s
biggest eye on the sky”.

Monday, November 28, 2016

Artist's conception of a shock-interacting supernova. Successive eruptions of a massive star produce ejecta with different velocities: the blue ring corresponds to slowly moving layers which are punched by fast ejecta (red-to-yellow) which shoots out. Interaction of those gas masses is via radiating shock waves which produce enormous amounts of light. This explains the phenomenon of Superluminous Supernovae with minimum requirements to the energy budget of explosions. (Credit: Kavli IPMU). Large Size jpg/Medium size jpg

Absolute u-band light curves for a fast-fading SLSN-I SN 2010gx and for a slowly fading one PTF09cnd are shown together with two calculated light curves for models N0 and B0 (from the paper by Sorokina et al.), which demonstrates that the interacting scenario can explain both narrow and broad light curves. The light curve of the typical (with “normal” luminosity) SN Ic, SN 1994I, is plotted for comparison. (Credit: Kavli IPMU).Large Size jpg/Medium size jpg

In a unique study, an international team of researchers including
members from the Kavli Institute for the Physics and Mathematics of the
Universe (Kavli IPMU) simulated the violent collisions between
supernovae and its surrounding gas— which is ejected before a supernova
explosion, thereby giving off an extreme brightness.

Many supernovae have been discovered in the last decade with peak
luminosity one-to-two orders of magnitude higher than for normal
supernovae of known types. These stellar explosions are called
Superluminous Supernovae (SLSNe).

Some of them have hydrogen in their spectra, while some others
demonstrate a lack of hydrogen. The latter are called Type I, or
hydrogen-poor, SLSNe-I. SLSNe-I challenge the theory of stellar
evolution, since even normal supernovae are not yet completely
understood from first principles.

Led by Sternberg Astronomical Institute researcher Elena Sorokina,
who was a guest investigator at Kavli IPMU, and Kavli IPMU Principal
Investigator Ken’ichi Nomoto, Scientific Associate Sergei Blinnikov, as
well as Project Researcher Alexey Tolstov, the team developed a model
that can explain a wide range of observed light curves of SLSNe-I in a
scenario which requires much less energy than other proposed models.

The models demonstrating the events with the minimum energy budget
involve multiple ejections of mass in presupernova stars. Mass loss and
buildup of envelopes around massive stars are generic features of
stellar evolution. Normally, those envelopes are rather diluted, and
they do not change significantly the light produced in the majority of
supernovae.

In some cases, large amount of mass are expelled just a few years
before the final explosion. Then, the “clouds” around supernovae may be
quite dense. The shockwaves produced in collisions of supernova ejecta
and those dense shells may provide the required power of light to make
the supernova much brighter than a “naked” supernova without pre-ejected
surrounding material.

This class of the models is referred to as “interacting” supernovae.
The authors show that the interacting scenario is able to explain both
fast and slowly fading SLSNe-I, so the large range of these intriguingly
bright objects can in reality be almost ordinary supernovae placed into
extraordinary surroundings.

Another extraordinarity is the chemical composition expected for the
circumstellar “clouds.” Normally, stellar wind consists of mostly
hydrogen, because all thermonuclear reactions happen in the center of a
star, while outer layers are hydrogenous.

In the case of SLSNe-I, the situation must be different. The
progenitor star must lose its hydrogen and a large part of helium well
before the explosion, so that a few months to a few years before the
explosion, it ejects mostly carbon and oxygen, and then explode inside
that dense CO cloud. Only this composition can explain the spectral and
photometric features of observed hydrogen-poor SLSNe in the interacting
scenario.

It is a challenge for the stellar evolution theory to explain the
origin of such hydrogen- and helium-poor progenitors and the very
intensive mass loss of CO material just before the final explosion of
the star. These results have been published in a paper accepted by The
Astrophysical Journal.

Ken’ichi Nomoto, Kavli Institute for the Physics and Mathematics of
the Universe, The University of Tokyo Institutes for Advanced Study,
The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583,
Japan

Alexey Tolstov, Kavli Institute for the Physics and Mathematics of
the Universe, The University of Tokyo Institutes for Advanced Study, The
University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan

Friday, November 25, 2016

This image of the spiral galaxy NGC 3274 comes courtesy of the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3
(WFC3). Hubble’s WFC3 vision spreads from the ultraviolet light through
to the near infrared , allowing astronomers to study a wide range of
targets, from nearby star formation through to galaxies in the most
remote regions of the cosmos.

This particular image combines observations gathered in five different filters,
bringing together ultraviolet, visible, and infrared light to show off
NGC 3274 in all its glory. As with all of the data Hubble sends back to
Earth, it takes advantage of the telescope’s location in space above our
planet’s distorting atmosphere. WFC3 returns clear, crisp, and detailed images time after time.

NGC 3274 is a relatively faint galaxy located over 20 million light-years away in the constellation of Leo (The Lion). The galaxy was discovered by Wilhelm Herschel in 1783. The galaxy PGC 213714 is also visible on the upper right of the frame, located much further away from Earth.